Digital line protection

ABSTRACT

A line protection device includes terminals to connect the line protection device in series with an electric line. A current sensor of the line protection device senses a value of electric current through the electric line. A digital filter circuit of the line protection device performs digital filtering of the value of electric current. Depending on the digitally filtered value of the electric current, a switch control circuit of the line protection device controls a switch to interrupt flow of the electric current through the line.

TECHNICAL FIELD

The present application relates to a line protection device and to amethod of line protection.

BACKGROUND

For protection of electric lines, such as wires, cables, conductorstrips, or connectors, it is known to use fuses, which prevent theelectric line from being damaged by excessive current flow.

Typically, a fuse is selected with characteristics which match a weakestelement of the electric line to be protected. In this respect, it needsto be considered that heating of the electric line will typically dependon the magnitude of electric current flowing through the electric lineand on a time duration for which the electric current is flowing throughthe electric line. That is to say, damage of the line may be caused by arelatively high electric current flowing for a relatively short timeduration or by a lower electric current flowing for a longer duration.This behavior may be represented in terms of a time-currentcharacteristic, e.g., given by the time duration of current flow as afunction of the magnitude of the current resulting in a maximumallowable temperature increase of the electric line. For example, in thecase of electrical cables a critical aspect is the temperature stabilityof an insulator of the cable. As a general rule, sensitivity of anelectric line depends on various parameters, such as line geometry,conductor material, and insulator material. Further, the sensitivitytypically also depends on ambient temperature of the electric line. Inview of the above situation, various types of fuses exist so that itbecomes possible to select a fuse which suits the characteristics of theelectric line to be protected.

Further, it is known to use electronic fuses. An electronic fuse may beimplemented on the basis of a semiconductor switch which is openeddepending on an electrical current flowing through the protectedelectric line. By way of example, US 2016/0109212 A1 describes anelectronic fuse device which also supports modelling of a fusecharacteristic by analog circuitry or by a software model. However,designing analog circuitry to achieve a certain fuse characteristic maybe a complex task. Further, implementing a software model of a fuse mayresult in increased complexity of the electronic fuse device.

Accordingly, there is a need for techniques which allow for efficientlyprotecting an electric line.

SUMMARY

According to an embodiment, a line protection device is provided. Theline protection device comprises terminals, a current sensor, a digitalfilter circuit, a switch control circuit, and a supply circuit. Theterminals are adapted to connect the line protection device in serieswith an electric line. The current sensor is adapted to a sense a valueof electric current through the electric line. The digital filtercircuit is adapted to perform digital filtering of the value of electriccurrent. The switch control circuit is adapted to control a switch tointerrupt flow of the electric current through the electric linedepending on the digitally filtered value of the electric current. Thesupply circuit is adapted to power at least the digital filter circuitfrom at least one of the terminals. The line protection device may alsocomprise the switch. However, it is also possible that the switch isprovided separately from the line protection device and controlled by asignal from the line protection device.

According to a further embodiment, a method of line protection isprovided. The method comprises connecting a line protection device inseries with an electric line. Further the method comprises sensing avalue of electric current through an electric line by a current sensorof the line protection device. Further, the method comprises digitalfiltering of the value of the electric current by a digital filtercircuit of the dine protection device. Further, the method comprisescontrolling a switch to interrupt flow of the electric current throughthe line depending on the digitally filtered value of the electriccurrent. Further, the method comprises powering at least the digitalfilter circuit from at least one terminal used to connect the lineprotection device in series with the electric line.

According to further embodiments of the invention, other devices,systems, or methods may be provided. Such embodiments will be apparentfrom the following detailed description in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A schematically illustrates a line protection device according toan embodiment of the invention.

FIG. 1B schematically illustrates a line protection device according toa further embodiment of the invention.

FIGS. 2A, 2B, 2C, and 2D schematically illustrate various scenarios inwhich an electric line is protected according to an embodiment of theinvention.

FIG. 3 schematically illustrates an electric line to which protectionaccording to an embodiment of the invention may be applied.

FIG. 4 shows an exemplary time-current characteristic of the electricline.

FIG. 5 schematically illustrates a configurable time-currentcharacteristic of a line protection device according to an embodiment ofthe invention.

FIG. 6 illustrates a thermal model of an electric line.

FIG. 7A further illustrates a digital filter circuit and switch controlcircuit of the line protection device.

FIG. 7B illustrates a further example of a digital filter circuit andswitch control circuit of the line protection device.

FIG. 8 shows an overall diagram of the line protection device with thedigital filter circuit and switch control circuit of FIG. 7B.

FIG. 9 shows a flowchart for schematically illustrating a method of lineprotection according to an embodiment of the invention.

DETAILED DESCRIPTION

In the following, various embodiments will be described in detail withreference to the accompanying drawings. It should be noted that theseembodiments serve only as examples and are not to be construed aslimiting. For example, while embodiments with a plurality of features,other embodiments may comprise less features and/or alternativefeatures. Furthermore, features from different embodiments may becombined with each other unless specifically noted otherwise.

Embodiments as illustrated in the following relate to protection of anelectric line, in particular to protecting the electric line from beingdamaged by excessive current flow. The electric line may for example bea wire, cable, conductor strip, or a connector. In the illustratedexamples, the electric line is protected by using a switch to interruptcurrent flow through the electric line before a damage of the electricline occurs. The switch is controlled depending on a digitally filteredvalue of the current through the electric line. The switch andelectronics for controlling the switch may be part of a line protectiondevice, e.g., in the form of an electronic fuse or in the form of aswitch device supplemented with a line protection function.

FIG. 1A schematically illustrates a line protection device 100 accordingto an embodiment. As illustrated, the line protection device 100 has twoterminals 101, 102 which are used to connect the line protection devicein series with an electric line 10 to be protected. The electric line 10may for example be or include a wire, cable, conductor strip, aconnector, or a combination thereof. In the illustrated example, theelectric line 10 is connected to a load R_(L). The load R_(L) may forexample include or be part of an electric motor, an electric lightingdevice, an electric heating or cooling device, or the like.

The line protection device 100 includes a switch 110, a current sensor120, a digital filter circuit 130, and a switch control circuit 140. Asfurther illustrated, the line protection device 100 may also include aparameter memory 160 and/or an interface 170.

The current sensor 120 is used to a sense a value of an electric currentI flowing through the electric line 10. The current sensor 120 providesthe sensed value of the electric current I to the digital filter circuit130. The digital filter circuit 130 performs digital filtering of thesignal representing the value of the electric current I and provides thedigitally filtered value of the electric current I to the switch controlcircuit 140. The switch control circuit 140 controls the switch 110depending on the digitally filtered value of the electric current I.Depending on the digitally filtered value of the electric current I,e.g., if the digitally filtered value of the electric current I exceedsa threshold, the switch control circuit 140 may control the switch 110to interrupt flow of the electric current I through the electric line10. The digital filtering of the value of the electric current I allowsfor triggering the interruption of the flow of the electric current Iaccording to a time-current characteristic which suits the electric line10 to be protected.

As further illustrated, the switch control circuit 140 may also receiveone or more additional input signals and control the switch 110 alsodepending on the additional input signal(s). In the illustrated example,the additional input signals include the unfiltered value of theelectric current I from the current sensor 120 and an input signal INprovided through a control input 103 of the line protection device 103.Based on the unfiltered value of the electric current I, the switchcontrol circuit 140 may for example interrupt flow of the electriccurrent I through the electric line 10 if the value of the electriccurrent I exceeds a threshold. Depending on the input signal IN, theswitch control circuit 140 may for example open or close the switch 110in a state where neither the digitally filtered value of the electriccurrent I nor the unfiltered value of the electric current I wouldtrigger interruption of the flow of the electric current I through theelectric line 10. In this way, the line protection device 100 may alsobe used as an externally controllable switch.

The supply circuit 150 is used to power components of the lineprotection device 100. Dotted lines in FIG. 1 schematically illustratethe powering of the components. For powering the components, the supplycircuit 150 derives electric power from at least one of the terminals101, 102 which are used to connect the line protection device 100 inseries with the electric line 10. In the illustrated example the supplycircuit 150 derives the electric power from a voltage applied at theterminal 101 and from a ground terminal 104 of the line protectiondevice 100. However, it is noted that in a similar manner the supplycircuit 150 could also derive the electric power from a voltage appliedat the terminal 102 and/or from a voltage applied at the terminal 101and a voltage applied at the terminal 102.

In the example of FIG. 1A, the supply circuit 150 is illustrated aspowering substantially all components of the line protection device 100.However, it is noted that in other scenarios some of the illustratedcomponents might not require powering by the supply circuit 150. Forexample, some components could be implemented by passive circuitelements and thus not require any powering. On the other hand, at leastthe digital filter circuit 130 is assumed to be implemented on the basisof active circuit elements and thus powered by the supply circuit 150.

The parameter memory 160 may be used for storing one or more filterparameters of the digital filter circuit 130 and/or one or more controlparameters of the switch control circuit 140. For example, the digitalfiltering performed by the digital filter circuit 130 could involvecalculation of a polynomial function, and the filter parameters coulddefine at least one polynomial coefficient of the polynomial function.Further, the digital filtering performed by the digital filter circuit130 could involve low-pass filtering, and the filter parameters coulddefine a cut-off frequency of said low-pass filtering. Further, thedigital filtering performed by the digital filter circuit 130 couldinvolve high-pass filtering, and the filter parameters could define acut-off frequency of said high-pass filtering. The control parameters ofthe switch control circuit 140 could for example define one or more ofthe above-mentioned thresholds.

At least a part of the filter parameter(s) and/or control parameter(s)may be preconfigured in the parameter memory 160, e.g., as part ofmanufacturer settings. However, it is also possible to utilize theinterface 170 to configure the filter parameter(s) and/or controlparameter(s). For example, the interface 170 could be used to selectbetween different parameter sets stored in the memory.

In the illustrated example, the interface 170 is provided with terminalsfor connecting an external configuration resistor R_(c), and the valueof the external configuration resistor R_(c) is used for indicatingwhich of the parameter sets is to be selected.

As an alternative or in addition to using the external configurationresistor R_(c), it would also be possible to provide the interface 170with one or more mechanical switch elements and to use the switchsettings to indicate which of the parameter sets is to be selected.Still further, it would be possible to provide the interface 170 withone or more data lines and to use the data lines to indicate which ofthe parameter sets is to be selected and/or to transfer the filterparameter(s) and/or control parameter(s) to the parameter memory 160. Inthis respect, it is also noted that for implementing a data line, theinterface could be equipped with one or more dedicated data lineterminals. However, it is also possible to reuse one or more otherterminals of the line protection device 100 to implement a data line,e.g., one or more of the terminals 101, 102, 103. In the latter case, adata signal which is transferred via the data line could be modulatedonto other signals applied at the reused terminal(s) 101, 102, 103.

In the example of FIG. 1A it was assumed that the switch 110 is part ofthe line protection device 100. However, it is also possible that theswitch 110 is an external component. FIG. 1B illustrates a correspondingembodiment of a line protection device 100′.

The line protection device 100′ is generally similar to the lineprotection device 100, and components of the line protection device 100′which correspond to those of the line protection device 100 have beendesignated by the same reference numerals. For further detailsconcerning these components, reference is made to the description withrespect to FIG. 1A.

In the case of the line protection device 100′, the switch controlcircuit 140 provides a control signal to an external switch 110′. Theline protection device 100′ and the external switch 110′ may be part ofthe same electronics package. Alternatively, the line protection device100′ and the external switch 110′ could be provided as separateelectronic packages.

In the example of FIG. 1B, the line protection device 100′ and theexternal switch 110′ are connected in series with the electric line 10to be protected, using the terminals 101, 102 of the line protectiondevice 100′. In this way, the electric current I through the electricline 10 can be sensed by the current sensor 120 of the line protectiondevice 100′.

For providing the control signal to the external switch 110′, the lineprotection device 100′ includes an output terminal 105. The switchcontrol circuit 140 of the line protection device 100 controls theswitch 110′ in the same way as explained above for the switch 110 of theline protection device 100. That is to say, the switch 110 is controlleddepending on the digitally filtered value of the electric current I.

FIGS. 2A, 2B, 2C, and 2D schematically illustrate various arrangementsof coupling the line protection device 100 to the electric line 10. Ascan be seen, in each of these arrangements the line protection device100 is connected in series with the electric line 10. In the arrangementof FIG. 2A, the line protection device 100 is connected to one end ofthe electric line 10, and in the arrangement of FIG. 2B, the lineprotection device 100 is connected to the other end of the electric line10. In the arrangement of FIG. 2C, the line protection device 100 isconnected between two segments of the electric line 10. In thearrangement of FIG. 2D, the line protection device 100 is connectedindirectly via an intermediate conductor element 20 to the electric line10. In each of these arrangements, the line protection device 100 can bepowered like explained above, by deriving power from at least one of theterminals 101, 102 used to connect the line protection device 100 inseries with the electric line 10. In each of these arrangements, theline protection device 100 may act as a replacement of a conventionalfuse.

The line protection device 100′ can be used in similar arrangements asillustrated in FIGS. 2A, 2B, 2C, and 2D. However, it is noted that inthis case the line protection device 100′ and the external switch 110′could be arranged at different locations. For example, the lineprotection device 100′ could be arranged at one end of the electric line10, like illustrated in FIG. 2A or 2B, while the external switch 110′ isarranged at the other end of the electric line 10 or is inserted betweentwo segments of the electric line 10.

As mentioned above, the digital filtering performed by the digitalfilter circuit 130 may be used to trigger the interruption of the flowof the electric current I according to a time-current characteristicwhich suits the electric line 10. This will be further explained in thefollowing.

FIG. 3 further illustrates exemplary properties of the electric line 10.In the illustrated example it is assumed that the electric line 10 is anisolated wire having a cylindrical geometry with an inner conductor 12covered by an insulator layer 14. The inner conductor 12, which may beformed by stranded or solid wire, has a diameter d1. The overalldiameter of the wire is d2. A thickness s of the insulator layer 14 isdenoted by s. The robustness of the electric line 10 depends on thesegeometric properties and also on constituent materials of the electricline 10, such as material of the conductor 12 and material(s) of theinsulator layer 14. A temperature limit T_(L) may be defined for theelectric line 10, e.g., as a temperature which should not be exceeded inorder to prevent damaging of the electric line 10.

When the electric current I flows through the electric line 10, heat isgenerated in the electric line 10. The resulting temperature of theelectric line 10 depends on various parameters, such as theabove-mentioned geometric properties of the electric line 10. Further,the resulting temperature also depends on the constituent materials ofthe electric line 10. Further, the resulting temperature also depends onthe value of the electric current I, time duration of current flowthrough the electric line 10, and on ambient temperature. As a generalrule, a higher value of the electric current I causes a higher resultingtemperature. Similarly, a higher duration of the current flow wouldcause a higher resulting temperature. This may be considered byrepresenting the robustness of the electric line 10 by a time-currentcharacteristic which, for a given ambient temperature, shows the time tto reach the temperature limit T_(L) of the electric line 10 as afunction of the value of the electric current I flowing through theelectric line 10. FIG. 4 shows an example of such time-currentcharacteristic. As can be seen, with increasing value of the electriccurrent I there is a shorter allowed time of current flow through theelectric line 10 until reaching the temperature limit T_(L). For lowvalues of the electric current I, the current may practically flow foran infinite time without reaching the temperature limit T_(L) beingreached.

To efficiently protect the electric line 10, it is desirable that theinterruption of the flow of the electric current I through the electricline 10 is triggered according to a characteristic which suits thetime-current characteristic of the electric line 10. Specifically,efficient protection may be achieved by triggering the interruption ofthe flow of the electric current I through the electric line 10according to a time-current characteristic which is similar to thetime-current characteristic of the electric line 10, but is shifted by amargin to towards lower currents and shorter times. This has the effectthat the flow of the electric current I through the electric line 10will be interrupted already before damage of the electric line 10occurs. In addition, it is also desirable to add overcurrent protectionby interrupting the flow of the electric current I through the electricline 10 when the value of the electric current I exceeds a certainmaximum threshold.

In the line protection device 100, 100′, the time-current characteristicfor triggering the interruption of the flow of the electric current I isimplemented by the digital filtering performed by the digital filtercircuit 130. The interruption in response to exceeding the maximumcurrent threshold may be implemented by the switch control circuit 140.FIG. 5 schematically illustrates the resulting combined characteristicfor interruption of the flow of the electric current I through theelectric line 10. For comparison, FIG. 5 illustrates the time-currentcharacteristic of the electric line 10 by a dotted line. As can be seen,the time-current characteristic provided by the line protection device100, 100′ can be regarded as having three branches: a firstsubstantially vertical branch defined by a lower current limit I₁, asecond substantially vertical branch defined by an upper current limitI₂, and a substantially horizontal branch which connects the twosubstantially vertical branches. Below the lower current limit I₁, alsoreferred to as maximum permanent current, the electric current I canflow for infinite time without triggering interruption of the flow ofthe electric current I. Above the upper current limit I₂, which is alsoreferred to as “trip current”, interruption of the flow of the electriccurrent I is triggered immediately, irrespective of the duration ofcurrent flow. A time position of the substantially horizontal branchrepresents a triggering speed or delay, denoted by T_(P).

FIG. 6 illustrates a thermal model of the electric line 10. Based onthis thermal model, it can be seen that the digital filtering of thevalue of the electric current through the electric line 10 can be usedto efficiently estimate the temperature of the electric line 10 from thevalue of the electric current I and thereby implement the a time-currentcharacteristic as explained in connection with FIG. 5.

In a cross-sectional view of the electric line 10, FIG. 6 shows thatheating of the electric line 10 can be modelled by defining a thermalresistance R_(th) and a thermal capacitance C_(th). The thermalresistance R_(th) describes an ability of conducting heat from the innerconductor 12 to an ambient medium surrounding the electric line 10,e.g., to ambient air. The thermal resistance R_(th) typically depends onthe thickness of the insulator layer 14, on the material(s) used in theconductor 12 and in the insulator layer 14, and also on the diameter d₁of the conductor 12 and the diameter d₂ of the electric line 10. Thethermal capacitance C_(th) parametrizes an ability of storing heat inthe electric line 10. Also the thermal capacitance C_(th) depends on thethickness of the insulator layer 14, on the material(s) used in theconductor 12 and in the insulator layer 14, and also on the diameter d₁of the conductor 12 and the diameter d₂ of the electric line 10.

Further, FIG. 6 also shows an equivalent thermal circuit which can beused to model heating of the electric line 10 due to the electriccurrent flowing through the electric line 10. As can be seen, theheating of the electric line 10 can be modelled in terms of a circuit inwhich a thermal dissipation power generated in the conductor 12 isapplied to a low-pass filter circuit defined by the thermal resistanceR_(th) and the thermal capacitance C_(th). The static behavior of theelectric line 10 in response to an electric current equal to the firstcurrent limit I1 can be described by the following equations:

P _(Dm) =k ₁ l ₁ +k ₂ l ₁ ²  (1)

P _(Dm) =k ₃ ΔT=k ₃(T _(L) −T _(A)),  (2)

where TL denotes the temperature limit defined for the electric line 10and T_(A) denotes the ambient temperature of the electric line 10. Thecoefficients k₁, k₂, k₃ depend on the properties of the electric line10.

The dynamic behavior of the electric line 10 in response to an electriccurrent above the first current limit I1 can in turn be described by thefollowing equations:

τ_(L) =R _(th) C _(th)  (3)

t _(S)=−τ_(L) ln(1−k ₃ ΔT/(k ₁ l+k ₂ l ²)),  (4)

where t_(S) denotes the time required for heating the electric line 10from the ambient temperature T_(A) to the temperature limit T_(L).

Accordingly, the thermal behavior of the electric line 10 can bedescribed in terms of two parameters: The current I1 which causesmaximum heating of the electric line 10 under static conditions, and atime constant τ_(P) which is defined by the thermal resistance R_(th)and the thermal capacitance C_(th). More specifically, the thermalbehavior of the electric line 10 in response to the electric current Iflowing through the electric line 10 can be modelled by calculating apolynomial function of the electric current I and subjecting the valuesof the polynomial function to low-pass filtering with a time constantτ_(L). In the line protection device 100, 100′, the time-currentcharacteristic for triggering interruption of the flow of the electriccurrent I through the electric line 10 can be configured to mimic thisthermal behavior, by performing digital filtering in the digital filtercircuit 130 which involves calculating a polynomial function of theelectric current I according to:

P=k ₁ l+k ₂ l ²  (5)

and then subjecting the output of the polynomial function to low-passfiltering with a time constant τ_(P). The output of the low-passfiltering represents a temperature increase with respect to the ambienttemperature T_(A). The time constant τ_(P) may be selected slightlylower than the time constant τ_(L) estimated for the electric line 10,to ensure that the interruption of the flow of the electric current istriggered before the electric line 10 can reach the temperature limitT_(L).

Assuming that the ambient temperature T_(A) is not available as ameasured input parameter, the ambient temperature T_(A) can be takeninto account in terms of a worst-case consideration, by assuming aworst-case ambient temperature T_(WC) which will not be exceeded undertypical operating conditions. The maximum permanent current, i.e., thelower current limit I₁, can then be used as a basis for estimating amaximum temperature T_(LS) of the electric line 10 under steadyconditions. For example, the maximum temperature T_(LS) of the electricline 10 under steady conditions could be estimated as

$\begin{matrix}{T_{LS} = {T_{WC} + {\frac{k_{2}}{k_{3}}{I_{1}^{2}.}}}} & (6)\end{matrix}$

In view of the above, digital filtering of the value of the electriccurrent I by the digital filter circuit 130 and logic evaluation of thedigitally filtered value of the electric current I by the switch controlcircuit 140 could be implemented as illustrated in FIG. 7A.

FIG. 7A shows a block diagram for illustrating an example of digitalfiltering operations performed by the digital filter circuit 130 on thebasis of a digitized value D(I) of the electric current I through theelectric line 10. Further, FIG. 7A shows an example of logic operationsperformed by the switch control circuit 140.

In the example of FIG. 7A, the digital filtering operations includecalculation of a polynomial function in filter block 710 and low-passfiltering in filter block 720. The logic operations include a comparisonin logic block 730, a comparison in logic block 740, and a logic oroperation in logic block 750.

The filter block 710 receives the digitized value D(I) of the electriccurrent I and digitally calculates a polynomial function according toequation (5). As shown by equation (5), the polynomial function may be asecond order polynomial function with non-zero coefficients k₁ and k₂for a linear part and a quadratic part of the polynomial function.However, in some implementations it would also be possible to neglectthe linear part and have a non-zero coefficient k₂ only for thequadratic part. However, having a non-zero coefficient k₁ also for thelinear part may allow for more accurately modelling that conductivity ofthe conductor 12 of the electric line 10 depends on temperature.

The output of the polynomial function is provided as a digital valueD(P) to the filter block 720. The filter block 720 performs digitallow-pass filtering of the output D(P) of the polynomial function. Forthis purpose, the filter block 720 may for example include a first orderdigital low-pass filter. However, utilization of a higher order digitallow-pass filter, e.g., second or third order, is possible as well. Theoutput of the filter block 720 represents the estimated temperatureincrease ΔT of the electric line 10, multiplied by the coefficient k₃.The output of the filter block 720 is provided as a digital valueD(k₃ΔT) to the logic block 730.

The logic block 730 receives the output D(k₃ΔT) of the filter block 720,i.e., the digitally filtered value of the electric current I, andcompares the output D(k₃ΔT) to a first threshold to decide whether theestimated temperature of the electric line 10 exceeds the temperaturelimit T_(L). Accordingly, the first threshold depends on the temperaturelimit T_(L). In addition the first threshold may depend on the ambienttemperature T_(A), e.g., in terms of an offset from the temperaturelimit T_(L). As explained in connection with equation (6) this offsetmay also be estimated on the basis of a worst case consideration fromthe maximum permanent current through the electric line 10.

If the logic block 730 decides that the estimated temperature of theelectric line 10 exceeds the temperature limit T_(L), the logic block730 sets an overtemperature signal OT to a digital value “1”. If thelogic block 730 decides that the estimated temperature of the electricline 10 does not exceed the temperature limit T_(L), the logic block 730sets the overtemperature signal OT to a digital value “0”.

The logic block 740 receives the digitized value D(I) of the electriccurrent I, i.e., the unfiltered value of the electric current I andcompares the value of the electric current I to a second threshold todecide whether the value of the electric current I exceeds the uppercurrent limit I₂, i.e., the trip current. The second current limit I₂may for example be set in view of protecting the line protection device100, 100′ itself from dissipating to much energy. Further, the secondcurrent limit I₂ may be set and also in view of protecting other devicescoupled to the electric line 10 from excessively high current peaks orin view of avoiding a supply voltage breakdown caused by such excessivecurrent peak.

If the logic block 740 decides that the value of the electric current Ithrough the electric line 10 exceeds the upper current limit I₂, thelogic block 740 sets an overcurrent signal OC to a digital value “1”. Ifthe logic block 740 decides that the value of the electric current Ithrough the electric line 10 does not exceed the upper current limit I₂,the logic block 740 sets the overcurrent signal OC to a digital value“0”.

The logic block 750 receives the overtemperature signal OT and theovercurrent signal OC and combines these two signals by a logic oroperation. That is to say, if at least one of the overtemperature signalOT and the overcurrent signal OC has the digital value “1”, the logicblock 750 sets a switch off signal SO to a digital value “1”. If none ofthe overtemperature signal OT and the overcurrent signal OC has thedigital value “1”, the logic block 750 sets the switch off signal SO toa digital value “0”. The switch off signal SO is then used fortriggering interruption of the flow the electric current I through theelectric line 10. Specifically, if the switch off signal SO is set tothe digital value “1”, the switch control circuit 140 interrupts theflow of the current I by opening the switch 110. If the switch offsignal SO is set to the digital value “0”, the switch control circuit140 may keep the switch 110 closed. However, depending on other criteriathe switch control circuit 140 may also open the switch when the switchoff signal SO is set to the digital value “0”, e.g., if theabove-mentioned external input signal IN indicates that the switch 110is to be opened.

In the example of FIG. 7A the digital filtering operations performed bythe digital filter circuit 130 include calculation of a polynomialfunction and low-pass filtering. However, it is noted that the digitalfilter circuit 130 may also implement other types of digital filteringoperations. FIG. 7B shows a block diagram for illustrating acorresponding example in which the digital filtering operationsperformed by the digital filter circuit 130 also include high-passfiltering. Further, FIG. 7B shows an example of further logic operationsperformed by the switch control circuit 140.

Also in the example of FIG. 7B the digital filtering operations includecalculation of a polynomial function in filter block 710 and low-passfiltering in filter block 720. The logic operations include a comparisonin logic block 730, a comparison in logic block 740, and a logic oroperation in logic block 750. Details concerning the operation of thefilter blocks 710 and 720 and the logic blocks 730, 740, and 750 can betaken from the above description in connection with FIG. 7A. In theexample of FIG. 7B, the digital filtering operations additionallyinclude high-pass filtering in filter block 760, and the logicoperations additionally include a comparison in logic block 770.

The filter block 760 receives the digitized value D(I) of the electriccurrent I and performs digital high-pass filtering of the value D(I).For this purpose, the filter block 760 may for example include a firstorder digital high-pass filter. However, utilization of a higher orderdigital high-pass filter, e.g., second or third order, is possible aswell. An output of the filter block 760 represents an estimate of thetime derivative dI/dt of the value of the electric current I through theline 10, multiplied by a coefficient k₄. The output of the filter block760 is provided as a digital value D(k₄ dI/dt) to the logic block 770.

The logic block 770 receives the output D(k₄ dI/dt) of the filter block760, i.e., the estimate of the time-derivative of the value of theelectric current I, and compares the output D(k₄ dI/dt) to a thirdthreshold (k₄ dI/dt)_(max) to decide whether there is an excessiveincrease of the electric current I through the electric line 10. Theexcessive increase of the electric current I may be indicative of ashort-circuit on the electric line 10.

If the logic block 770 decides that there is an excessive increase ofthe electric current I through the electric line 10, the logic block 770sets a short-circuit signal SC to a digital value “1”. Otherwise, thelogic block 770 sets the short circuit signal SC to a digital value “0”.

In the example of FIG. 7B, the logic block 750 receives theovertemperature signal OT, the overcurrent signal OC, and the shortcircuit signal SC and combines these three signals by a logic oroperation. That is to say, if at least one of the overtemperature signalOT, the overcurrent signal OC, and the short circuit signal SC has thedigital value “1”, the logic block 750 sets a switch off signal SO to adigital value “1”. If none of the overtemperature signal OT, theovercurrent signal OC, and the short circuit signal SC has the digitalvalue “1”, the logic block 750 sets the switch off signal SO to adigital value “0”. Similar to the example of FIG. 7A, the switch offsignal SO is then used for triggering interruption of the flow theelectric current I through the electric line 10. Specifically, if theswitch off signal SO is set to the digital value “1”, the switch controlcircuit 140 interrupts the flow of the current I by opening the switch110. If the switch off signal SO is set to the digital value “0”, theswitch control circuit 140 may keep the switch 110 closed. However,depending on other criteria the switch control circuit 140 may also openthe switch when the switch off signal SO is set to the digital value“0”, e.g., if the above-mentioned external input signal IN indicatesthat the switch 110 is to be opened.

In the example of FIG. 7B, the processing of the digital value D(I) byhigh-pass filtering in the filter block 760 and comparison to thethreshold value in the logic block 770 allows for also interrupting theflow of the electric current I through the electric line 10 when a shortcircuit on the electric line 10 causes an abrupt increase of the valueof the electric current I. In this case, the interruption of the flow ofthe electric current I can be triggered early, already before there issignificant heating of the electric line 10 and before the upper currentlimit I₂ is reached. In this way, protection of the electric line 10 inshort-circuit scenarios can be further improved.

It is noted that in a variant of the example of FIG. 7B the output D(P)of the filter block 710 could be used instead of the digital value D(I)as the input of high-pass filtering in filter block 760. In stillanother variant, the low-pass filtering of filter block 720 and thehigh-pass filtering of filter block 760 could be implemented by the samefilter block, e.g., by providing the filter block 720 with a band-stopfilter characteristic. In the latter case, the output of the filterblock 720 could be provided both to the logic block 730 and to the logicblock 770.

FIG. 8 shows an overall block diagram for illustrating how theabove-mentioned functionalities of the line protection device 100, 100′can be implemented by electronic circuit elements. Similar to FIG. 1,FIG. 8 uses dotted lines to schematically illustrate powering ofcomponents of the line protection device 100, 100′.

In the example of FIG. 8, the line protection device 100, 100′ and theline 10 to be protected are supplied from a voltage source 800, e.g., abattery. The line protection device 100, 100′ includes a transistor 810.The transistor may implement the internal switch 110 of FIG. 1A or theexternal switch 110 of FIG. 1B. The transistor 810 may for example be anMOSFET (Metal Oxide Semiconductor Field Effect) transistor, e.g., apower MOSFET based on a DMOS technology (Double Diffused Metal Oxide) orVMOS (V-groved Metal Oxide Semiconductor) technology. However, othertransistor types could be used as well. The voltage source 800, thetransistor 810, the electric line 10 to be protected, and the load R_(L)are connected in series. Accordingly, if the transistor 810 is in aconducting state, the electric current I through the electric line 10will also flow through the transistor 810. By bringing the transistor810 into a non-conducting state, the flow of the electric current Ithrough the electric line 10 can be interrupted.

Further, the line protection device 100, 100′ includes a gate driver 820which generates a gate signal V_(G) for controlling the transistor 810to change between the conducting state and the non-conducting state. Thegate driver 820 is powered by an input voltage provided by the voltagesource 800. Accordingly, the same terminals which are used to connectthe transistor in series with the voltage source 800 can also be used topower the gate driver 820.

As illustrated by the dotted lines, the gate driver 820 also suppliespower to other components of the line protection device 100, 100′. Forexample, the gate driver 820 could derive one or more supply voltagesV_(S) from the input voltage provided by the voltage source 800 anddistribute the supply voltage(s) V_(S) to the other components asillustrated by the dotted lines.

In the illustrated example, it is assumed that the transistor 810 is ofa “normally off” type. That is to say, the gate signal V_(G) needs to beactively generated with a certain voltage level, above a thresholdvoltage of the transistor 810, to bring the transistor 810 into theconducting state. In this way, a the line protection device 100, 100′can be operated in a fail-safe manner, by ensuring that in cases wherethe line protection device 100, 100′ is not active due to a lack ofpower, the transistor 810 is in the non-conducting state and here can beno electric current I through the electric line 10 to be protected.

In the example of FIG. 8, the line protection device 100, 100′ furtherincludes a shunt resistor R_(S) and a voltage sensor 830. The shuntresistor R_(S) is connected in series between the transistor 810 and theelectric line 10. The voltage sensor 830 senses a voltage level on eachterminal of the shunt resistor R_(S), and these voltage levels areprovided through a level shifter 840 to a measurement amplifier 850. Themeasurement amplifier 850 provides a single-ended output voltage whichrepresents the voltage across the shunt resistor R_(S) and thus thevalue of the electric current I through the electric line 10.

The output voltage of the measurement amplifier 850 is fed to ananti-aliasing filter 860. The anti-aliasing filter 860 may for examplehave a low-pass characteristic. The output of the anti-aliasing filter860 is supplied to an adder 870 which adds a half-signal range offset toits input signal. The output signal of the adder 870 is then supplied toan analog-digital converter 880 for analog-to-digital conversion. Adigital output of the analog-digital converter 880 is then supplied to afurther adder 890 which digitally subtracts the half-range signal offsetfrom the digital output of the analog-digital converter 880. By addingthe half-signal range offset before analog-to-digital conversion andsubtracting the half-signal range offset after analog-to-digitalconversion, conversion of the value of the electric current I into adigital value can be supported for both polarities of the electriccurrent I.

In addition, subtraction of the offset after analog-to-digitalconversion can also be used for correcting other offsets. For example,due to manufacturing tolerances the voltage sensor 830, the levelshifter 840, the measurement amplifier 850, the anti-aliasing filter860, or the adder 870 may introduce an offset to the output of theanalog-digital converter 880. This offset can be estimated byshort-circuiting the inputs of the voltage sensor 830 and measuring theoffset in terms of the resulting digital output of the analog-to-digitalconverter 880. During normal operation of the line protection device100, 100′, the measured offset can then be additionally subtracted bythe adder 890.

In combination, the shunt resistor R_(S), the voltage sensor 830, thelevel shifter 840, the measurement amplifier 850, the anti-aliasingfilter 860, the adder 870, the analog-to-digital converter 880, and theadder 890 may implement the current sensor 120. In the illustratedexample, the current sensor 120 would thus be configured to sense thevalue of the electric current I through the electric line 10 and outputa digital value representing the value of the electric current I, suchas the above-mentioned digital value D(I). However, it is noted thatother implementations of the current sensor 120 could be used as well.For example, the current sensor 120 could also be implemented completelyon the basis of analog circuitry, and analog-to-digital conversion couldbe performed by an input stage of the digital filter circuit 140.

In the example of FIG. 8, it is assumed that the digital value D(I)representing the value of the electric current I is then processed asexplained in connection with FIG. 7B to generate the switch of signalSO. That is to say, the digital value D(I) is processed by the filterblocks 710, 720, and 760, and the logic blocks 730, 740, 750, and 770.However, it is noted that the filter block 760 and the logic block 770could also be omitted and the switch off signal SO could be generated asexplained in connection with FIG. 7A.

The switch of signal SO is supplied to the gate driver 820 and used totrigger interruption of the flow of the electric current I when theswitch of signal SO is set to the digital value “1”. In the example ofFIG. 8 this means that in response to the switch off signal SO havingthe digital value “1”, the gate driver 820 will stop generating the gatesignal V_(G) with the required voltage level to bring the transistor 810into the conducting state.

In the example of FIG. 8, the gate driver 820 also receives the externalinput signal IN. While the switch off signal SO has the digital value“0”, the gate driver 820 may generate the gate signal V_(G) to switchthe transistor 810 between the conducting state and the non-conductingstate, so that the line protection device 100 can also be used forimplementing an externally controllable switch. Here, it is noted thatwhen the switch off signal SO has the digital value “1”, the gate driver820 will always bring the transistor 810 into the non-conducting stateand interrupt the flow of the electric current I. In this way, it can beavoided that the transistor 810 is brought back into the conductingstate before the electric line 10 has sufficiently cooled down. Aftertriggering interruption of the flow of the electric current I by theswitch of signal SO, the switch of signal SO can be latched by the gatedriver 820 so that the transistor 810 remains in the non-conductingstate until the line protection device 100, 100′ is reset. Resetting ofthe line protection device 100, 100′ can for example require applying aspecific signal sequence to the external input signal IN ordisconnecting the line protection device 100, 100′ from the voltagesource 800. In some cases, the line protection device 100, 100′ couldalso be automatically reset by latching the switch of signal SO only fora limited time.

The above-mentioned parameter memory 160 may include various parametersfor configuring the operation of the line protection device 100, 100′ asexplained in connection with FIGS. 7 and 8. These parameters may bestored as part of manufacturer settings, e.g., during end-testing of theline protection device 100, 100′. However, it is also possible that atleast some of these parameters are configurable by a user of the lineprotection device 100, 100′, e.g., using the above-mentioned interface170.

The parameter memory 160 may include values for the coefficients k₁, k₂,k₃, k₄, the time constant τ_(P) of low-pass filtering in the filterblock 720, and/or the time constant T_(H) of high-pass filtering in thefilter block 760. Further, the parameter memory 160 may define thethreshold values to be used by the logic blocks 730 and 740. In the caseof the logic block 730, the first threshold value could for example bedefined in terms of a maximum allowable temperature increase ΔT_(m), interms of k₃ΔT_(m), or in terms of k₃(T_(L)−T_(A)). However, the firstthreshold value could also be defined in terms of the temperature limitT_(L) and a worst-case estimate of the ambient temperature T_(A) basedon the maximum permanent current I₁. Still further, the parameter memory160 could also include different options for the first threshold value,which could be selected according to a measurement of the ambienttemperature T_(A) or according to an estimated range of the ambienttemperature T_(A).

In some scenarios, the linear term of the polynomial functionimplemented by the filter block 710 can be neglected. In this case, thedigital processing performed by the filter block 710 and 720 can besimplified. In particular, the filter block 710 could then be configuredto merely perform squaring of the digital value D(I), and the remainingcoefficients k₂ and k₂ could be combined to a single coefficientk=k₃/k₂. The first threshold value could then be defined in terms ofkΔT_(m) or in terms of k(T_(L)−T_(A)).

FIG. 9 shows a flowchart for illustrating a method which may be used forimplementing the concepts as described in the foregoing. The method mayfor example be performed with the above-mentioned line protection device100 or 100′.

At 910, a line protection device is connected in series with an electricline, such as the above-mentioned electric line 10. This may beaccomplished by using terminals of the line protection device, such asthe above-mentioned terminals 101 and 102. At least one of the terminalsis used to power components of the line protection device.

At 920, a current sensor of the line protection device senses a value ofan electric current through the electric line. The current sensor mayfor example correspond to the above-mentioned current sensor 120 and beimplemented by a shunt resistor and a voltage sensor, like explained inconnection with FIG. 8. Further, the current sensor may include at leastone of: a level shifter, a measurement amplifier, an anti-aliasingfilter, and an analogue-to-digital converter.

At 930, a digital filter circuit performs digital filtering of the valueof the electric current. The digital filtering performed by the digitalfilter circuit may involve low-pass filtering, such as explained inconnection with filter block 720. Alternatively or in addition, thedigital filtering performed by the digital filter circuit may involvehigh-pass filtering, such as explained in connection with filter block760. Further, the digital filtering performed by the digital filtercircuit may involve calculating a polynomial function of the value ofthe electric current, such as explained in connection with filter block710. The digital filtering performed by the digital filter circuit maythen involve low-pass filtering of the calculated polynomial function.The polynomial function may be a second order polynomial function. Atthe second order polynomial function may have a non-zero linear part anda non-zero quadratic part. However, in some scenarios the second orderpolynomial function could only have a non-zero quadratic part.

The digital filter circuit may perform the digital filtering on thebasis of one or more configurable filter parameters. Such filterparameters may for example include one or more coefficients of thepolynomial function, such as the above-mentioned coefficient k₁ or k₂, atime constant of low-pass filtering, such as the above-mentioned timeconstant τ_(P), or a time constant of high-pass filtering, such as theabove-mentioned time constant τ_(H). The filter parameters may beconfigurable through an interface of the line protection device, such asthe above-mentioned interface 170.

At 940, a switch is controlled depending on the digitally filtered valueof the electric current. The switch may be an internal switch of theline protection device, such as the above-mentioned switch 110.Alternatively, the switch may be an external switch, such as theabove-mentioned switch 110′. In the latter case the external switch maybe controlled by a control signal output from the line protectiondevice. Depending on the digitally filtered value of the electriccurrent, the switch is controlled to interrupt flow of the electriccurrent through the electric line.

The switch may be controlled depending on a comparison of the digitallyfiltered value of the electric current to a first threshold, such as forexample explained in connection with logic block 730 or logic block 770.Further, the switch may be controlled depending on a comparison of thevalue of the electric current to a second threshold, such as for exampleexplained in connection with logic block 740. Further, the switch may becontrolled depending on an input signal to interrupt the current flowindependently of the value of the electric current, such as for exampleexplained in connection with the above-mentioned external input signalIN.

The switch may be controlled on the basis of one or more configurablecontrol parameters. Such control parameters may for example define theabove-mentioned first threshold and/or the above-mentioned secondthreshold. The control parameters may be configurable through aninterface of the line protection device, such as the above-mentionedinterface 170.

In the method of FIG. 9, at least the digital filter circuit is poweredfrom the at least one terminal used to connect the line protectiondevice in series with the electric line. However, also other componentsof the line protection device could be powered from the at least oneterminal, such as the current sensor or a switch control circuitconfigured to implement the control operations performed at 940.

It is to be understood that the above-described concepts and embodimentsare susceptible to various modifications. For example, the illustratedline protection devices may be implemented on the basis of various typesof circuit technology. Further, the illustrated line protection devicesand line protection methods could be applied in various applicationenvironments, e.g., in the automotive field, in industrial productionsystems, in home appliances, or home electronic devices.

Some non-limiting embodiments are provided according to the followingexamples.

Example 1

A line protection device, comprising:

-   -   terminals adapted to couple the line protection device in series        with an electric line;    -   a current sensor adapted to a sense a value of an electric        current through the electric line;    -   a digital filter circuit adapted to perform digital filtering of        the value of electric current;    -   a switch control circuit adapted to control a switch to        interrupt flow of the electric current through the electric line        depending on the digitally filtered value of the electric        current; and    -   a supply circuit adapted to power at least the digital filter        circuit from at least one of the terminals.

Example 2

The line protection device according to example 1,

wherein said digital filtering comprises low-pass filtering.

Example 3

The line protection device according to example 1 or 2,

wherein said digital filtering comprises high-pass filtering.

Example 4

The line protection device according to any one of the precedingexamples,

wherein said digital filtering comprises calculating a polynomialfunction of the value of the electric current.

Example 5

The line protection device according to example 4,

wherein said digital filtering comprises low-pass filtering of thecalculated polynomial function.

Example 6

The line protection device according to any one of the precedingexamples,

wherein the switch control circuit is adapted to control the switchdepending on a comparison of the digitally filtered value of theelectric current to a first threshold.

Example 7

The line protection device according to any one of the precedingexamples,

wherein the switch control circuit is adapted to control the switchdepending on a comparison of the value of the electric current to asecond threshold.

Example 8

The line protection device according to any one of the precedingexamples,

wherein the switch control circuit is adapted to control the switchdepending on an input signal to interrupt the electric currentindependently of the value of the electric current.

Example 9

The line protection device according to any one of the precedingexamples,

wherein the digital filter circuit is adapted to operate on the basis ofone or more configurable filter parameters.

Example 10

The line protection device according to any one of the precedingexamples,

wherein the switch control circuit is adapted to operate on the basis ofone or more configurable control parameters.

Example 11

The line protection device according to any one of the precedingexamples,

wherein the line protection device comprises the switch.

Example 12

A method of line protection, comprising:

-   -   coupling a line protection device in series with an electric        line;    -   sensing a value of an electric current through the electric line        by a current sensor of the line protection device;    -   digital filtering of the value of the electric current by a        digital filter circuit of the line protection device;    -   depending on the digitally filtered value of the electric        current, controlling a switch to interrupt flow of the electric        current through the electric line; and    -   powering the digital filter circuit from at least one terminal        used to connect the line protection device in series with the        electric line.

Example 13

The method according to example 12,

wherein said digital filtering comprises low-pass filtering.

Example 14

The method according to example 12 or 13, wherein said digital filteringcomprises high-pass filtering.

Example 15

The method according to any one of examples 12-14,

wherein said digital filtering comprises calculating a polynomialfunction of the value of the electric current.

Example 16

The method according to example 15,

wherein said digital filtering comprises low-pass filtering of thecalculated polynomial function.

Example 17

The method according to any one of examples 12-16, comprising:

-   -   controlling the switch depending on a comparison of the        digitally filtered value of the electric current to a first        threshold.

Example 18

The method according to any one of examples 12-17, comprising:

-   -   controlling the switch depending on a comparison of the value of        the electric current to a second threshold.

Example 19

The method according to any one of examples 12-18, comprising:

-   -   controlling the switch depending on an input signal to interrupt        the current flow independently of the value of the electric        current.

Example 20

The method according to any one of examples 12-19, comprising:

-   -   performing said digital filtering on the basis of one or more        configurable filter parameters.

Example 21

The method according to any one of examples 12-20,

-   -   controlling the switch on the basis of one or more configurable        control parameters.

In view of the many variations and modifications discussed above, it isevident that the embodiments are not to be construed as limiting thescope of the present application in any way.

What is claimed is:
 1. A line protection device, comprising: terminalsadapted to couple the line protection device in series with an electricline; a current sensor adapted to a sense a value of an electric currentthrough the electric line; a digital filter circuit adapted to performdigital filtering of the value of electric current; a switch controlcircuit adapted to control a switch to interrupt flow of the electriccurrent through the electric line depending on the digitally filteredvalue of the electric current; and a supply circuit adapted to power atleast the digital filter circuit from at least one of the terminals. 2.The line protection device according to claim 1, wherein said digitalfiltering comprises low-pass filtering.
 3. The line protection deviceaccording to claim 1, wherein said digital filtering comprises high-passfiltering.
 4. The line protection device according to claim 1, whereinsaid digital filtering comprises calculating a polynomial function ofthe value of the electric current.
 5. The line protection deviceaccording to claim 4, wherein said digital filtering comprises low-passfiltering of the calculated polynomial function.
 6. The line protectiondevice according to claim 1, wherein the switch control circuit isadapted to control the switch depending on a comparison of the digitallyfiltered value of the electric current to a first threshold.
 7. The lineprotection device according to claim 1, wherein the switch controlcircuit is adapted to control the switch depending on a comparison ofthe value of the electric current to a second threshold.
 8. The lineprotection device according to claim 1, wherein the switch controlcircuit is adapted to control the switch depending on an input signal tointerrupt the electric current independently of the value of theelectric current.
 9. The line protection device according to claim 1,wherein the digital filter circuit is adapted to operate on the basis ofone or more configurable filter parameters.
 10. The line protectiondevice according to claim 1, wherein the switch control circuit isadapted to operate on the basis of one or more configurable controlparameters.
 11. The line protection device according to claim 1, whereinthe line protection device comprises the switch.
 12. A method of lineprotection, comprising: coupling a line protection device in series withan electric line; sensing a value of an electric current through theelectric line by a current sensor of the line protection device; digitalfiltering of the value of the electric current by a digital filtercircuit of the line protection device; depending on the digitallyfiltered value of the electric current, controlling a switch tointerrupt flow of the electric current through the electric line; andpowering the digital filter circuit from at least one terminal used toconnect the line protection device in series with the electric line. 13.The method according to claim 12, wherein said digital filteringcomprises low-pass filtering.
 14. The method according to claim 12,wherein said digital filtering comprises high-pass filtering.
 15. Themethod according to claim 12, wherein said digital filtering comprisescalculating a polynomial function of the value of the electric current.16. The method according to claim 15, wherein said digital filteringcomprises low-pass filtering of the calculated polynomial function. 17.The method according to claim 12, comprising: controlling the switchdepending on a comparison of the digitally filtered value of theelectric current to a first threshold.
 18. The method according to claim12, comprising: controlling the switch depending on a comparison of thevalue of the electric current to a second threshold.
 19. The methodaccording to claim 12, comprising: controlling the switch depending onan input signal to interrupt the current flow independently of the valueof the electric current.
 20. The method according to claim 12,comprising: performing said digital filtering on the basis of one ormore configurable filter parameters.
 21. The method according to claim12, controlling the switch on the basis of one or more configurablecontrol parameters.